Volume 12, Issue 16                                                                     July 9, 2004



Vegetable Crop Insects - Joanne Whalen, Extension  IPM Specialist;   jwhalen@udel.edu


Blacklight and Pheromone Trap Catches.
Although trap catches have been generally light this season, with a few peaks in corn borer catches, we are starting to see an increase in corn borer and corn earworm trap catches. Trap catches are updated twice a week (generally Monday and Thursday PM late) on our website (http://www.udel.edu/IPM/traps/latestblt.html) or on the Crop Pest Holtline (1-800-345-7544 – in state only or 1-302-831-8851 – out of state).

Lima Beans.
Continue to watch for spider mites on seedling stage lima beans, especially in areas of the state that have not been receiving adequate rainfall. Both field interiors as well as field edges should be examined for mites. Look for the white stippling along the veins on the underside of the leaves. A treatment should be considered when you first notice the stippling and you find 10-20 mites per leaflet. Kelthane or Capture (6.4 oz/A) have provided the best control in lima beans when infestations are caught early; however, multiple treatments are generally needed.  The earliest planted field with pin pods should be scouted for lygus bugs and stinkbugs. Treatment should be considered if you find 15 adults and/or nymphs per 50 sweeps. Lannate, Capture or Mustang can be used if both species are present. The higher labeled rates of Capture (4 oz/A) and Mustang (4.3 oz/A) will be needed if stinkbugs are the predominant insect present.

Continue to scout all melons for aphids, cucumber beetles, and spider mites. We continue to see an increase in the number of fields with spider mite and aphid infestations. If spider mite populations are high at the time of treatment, 2 sprays spaced 5 days apart will be needed. The threshold for mites is 20-30% infested crowns with 1-2 mites per leaf. Acramite (only one application per season), Capture, Danitol, Agri-Mek or Kelthane will provide control, but should be rotated to avoid the development of resistance. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Be sure to check runners carefully for aphids.  For a treatment to be effective, fields should be sprayed before you see significant leaf curling.  Be sure to watch for bees foraging in the area and avoid insecticide applications on blooming crops. 

In areas where corn borer trap catches are above 2 per night and pepper fruit is ½ inch in size or larger, fields should be sprayed on a 7-10 day schedule for corn borer control.  You will also need to consider a treatment for pepper maggot. If Orthene is used, it will also provide pepper maggot control. Otherwise, dimethoate should be added to the mix. You should also watch for beet armyworm (BAW) larvae. No threshold is available, so you need to watch for the first small larvae as well as their feeding. You will also need to use a product like Confirm, Spintor, Avaunt or Intrepid which provide good BAW control.

Continue to scout fields on a weekly basis for Colorado potato beetle (CPB) adults and larvae. We continue to find economic levels of  green peach aphids in fields that did not receive Admire, Platinum or Tops MZ Gaucho at planting. A control will be needed if you find 2 aphids per leaf pre- bloom, 4 aphids per bloom – post bloom and 10 aphids per leaf at 2 weeks from vine kill/harvest.  If melon aphids are found, the threshold should be reduced by ½.  If green peach aphid is the predominant species, Fulfill, Lannate, Monitor, Provado, or Vydate will provide control. If Fulfill is used, a penetrating surfactant is needed to achieve good coverage and achieve optimum control.

Snap Beans.
ll seedling stage beans should be scouted for leafhopper and thrips activity. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by 1/3. Dimethoate, Lannate, Asana, Capture, or Warrior will provide control of both insect pests. Once corn borer catches reach 2 per night, fresh market and processing snap beans in the bud to pin stages should be sprayed for corn borer. Acephate should be used at the bud and pin stages on processing beans. Once pins are present on fresh market snap beans and trap catches are above 2 per night, a 7-10 day schedule should be maintained for corn borer control.  Lannate, Asana, Capture, Warrior or Mustang are labeled. Acephate has a 14-day wait until harvest. Since this can change quickly, be sure to check our website for the most recent trap catches and information on how to use this information to make a treatment decision in processing snap beans  (http://www.udel.edu/IPM/traps/latestblt.html and http://www.udel.edu/IPM/thresh/snapbeanecbthresh.html).

Sweet Corn
All fresh market silking sweet corn should be sprayed on a 4-5 day schedule except in the Dover, Milford, Greenwood and Seaford areas where sprays are needed on a 3-day schedule.  Since this information can change quickly, be sure to check our website for the most recent trap catches and information on how to use this information to make a treatment decision in silking sweet corn (http://www.udel.edu/IPM/traps/latestblt.html and http://www.udel.edu/IPM/thresh/silkspraythresh.html).  You should also watch for fall armyworm feeding in the whorls. A treatment is needed if you find 12-15% of the plants infested. Generally, 2-3 whorl sprays are needed to achieve control. In whorl stage corn, Avaunt, Lannate, Larvin and the high rate of Warrior have provided the best control in recent years. However, worms must be small at treatment time to achieve effective control.



Post-emergence Weed Control In Lima Beans Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu


Basagran is an effective material for many broadleaf weeds in lima beans.  The rate is 1 to 2 pints/acre.  The youngest stage of the lima bean for application is a fully expanded first trifoliate leaf.  Do not spray if the beans are younger than this.  Use the lower rate to control common cocklebur, mustards, and jimsonweed.  The higher rate will control yellow nutsedge, common lambsquarter (the smaller the better), common ragweed, and Canada thistle. 


Sprays should include crop oil, or to reduce the risk of crop injury, use a non-ionic surfactant.  Do not spray when temperatures are over 90oF.  Weeds are better controlled when small.



pH Problems on MelonsDerby Walker, Sussex County Extension Ag Agent, derby@udel.edu


In the last 10 days we have seen 4 cantaloupe fields with low ph problems. Cantaloupes are more sensitive then watermelons. Watermelons will tolerate a pH down to 5.5, where as, cantaloupes require a pH of 6.0.  We have two big issues, manganese toxicity and calcium deficiency.  Even with adequate calcium, you can create a calcium problem with an inadequate watering program. Dry soil reduces root growth, increases salt concentration, and can change cation ratios. These reduce calcium uptake because of the lack of new roots to obtain more calcium. Even our fertilizer program can create calcium problems. Potassium and ammonium nitrogen compete with calcium uptake in the plant.  Over application of these products, especially with a less then adequate watering program, can lead to a calcium problem. This deficiency will generally be seen as an increase in fruit decay problems. If calcium deficiency is severe enough, you can have foliar symptoms. Using an annual soil test program is very important in managing sensitive crops to insure a balanced nutrient program. Too much of a good thing can will increase your costs, as well as  cost you money in lost marketable yields, a double whammy.



Vegetable Crop Diseases - Bob Mulrooney, Extension Plant Pathologist, bobmul@udel.edu


Late Blight Advisory.


Disease Severity Value (DSV) Accumulation as of July 7, 2004 is as follows:

Location: Joe Jackewicz Farm, Magnolia, DE. Greenrow: April 25, 2004




Daily DSV


Total DSV

Spray Recommendation

4/25- 5/18

























































































What is driving the spray recommendation at the present time is the need for fungicides for early blight control. Conditions have not been favorable for late blight.


Application rates for protectant fungicides (Dithane, Bravo, etc.) should be at the high end of the rate with the amount of foliage present.


For specific fungicide recommendations for early blight and late blight, see pages F132-33, 2004 Delaware Commercial Vegetable Production Recommendations Book. EB 137.


ALERT.   On, July 1, 2004 Alan MacNab, Vegetable Pathologist at Penn State reported Late Blight was confirmed in Lancaster county on tomatoes and he is checking additional reports.  There are also reports of Late Blight on potatoes in Erie County, PA and in New York.  In any case, potato fields in Delaware should be protected from this disease immediately.  If you have not applied any fungicide begin applying a protectant fungicide. If you have applied a protectant fungicide you should continue based on this potato disease update.  Weather conditions have not been favorable in Kent and Sussex, but New Castle County growers and those with acreage in nearby Maryland may be more at risk from late blight.




Vegetable Crop Diseases – Kate Everts, Extension Plant Pathologist, University of Maryland and University of Delaware, everts@udel.edu


Downy Mildew on Cucurbits.

Downy mildew may cause severe damage to cucurbits when the disease is present and weather is conducive for disease development.  Cucurbit growers should be intensive in scouting for downy mildew.  Dr. Gerald Holmes from North Carolina State University reports that downy mildew on North Carolina cucumbers is especially severe this year.  The pickling cultivars ‘Vlasstar’ and ‘Jackson’ and the long greens ‘Speedway’ and ‘Dasher II’ appeared to have some resistance in NCSU trials.  Downy mildew spores are transported to Delaware and Maryland on upper air currents from infected cucurbit fields in the southern U.S. (often North Carolina).  Therefore the risk of downy mildew development is high.  The use of preventative fungicide applications on cucurbits is important in management of downy mildew.  Chlorothalonil (Bravo or Echo), Tanos, Ridomil Gold/Bravo, Flouronil, Cabrio, Pristine and Gavel have good efficacy on downy mildew when used properly (see the labels for guidelines).



Field Crops

Field Crop Insects - Joanne Whalen, Extension  IPM Specialist; jwhalen@udel.edu



Continue to sample all fields on a weekly basis for potato leafhopper (PLH) adults and nymphs.With the current weather patterns, sprays may be needed on multiple cuttings. Remember, controls are most critical on small plants. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa.

Spider mite populations started to explode at the end of last week, so watch fields carefully for mites.  We continue to see an increase in fields with visible spider mite damage, especially drought stressed fields. It will be important to scout the entire field before deciding if an edge treatment is enough.  Early treatment is needed to achieve control – once significant yellowing occurs it will be extremely difficult to achieve control and multiple treatments will be needed.   A treatment is recommended if you find 20-30 mites per leaflet or 10% of plants with 1/3 or more leaf area damaged. At this point, the only materials available for mite control in soybeans are dimethoate and Lorsban.  If dimethoate is used, the addition of a penetrating surfactant like LI-700 or Penetrator plus,or a material like Helena’s Hyperactive should be used to improve control, especially in drought stressed fields. Multiple applications may be needed 5-7 days apart.  At this point, dimethoate has been providing about 80% control. However, in fields that had mites present in the cotyledon, some are on their third application in Maryland. Remember, Lorsban only provides contact control, so multiple applications are needed 5-7 days apart.  The addition of a crop oil has also improved control with Lorsban when applied by air. We have submitted a Section 18 Specific Exemption Request to EPA for the use of Acramite. This material is a true miticide, has activity on the motile stages and is known to be ovicidal on spider mite eggs.  At this time, we are not asking for a Section 18 Crisis Exemption, since there is no tolerance for the product (like all Sect 18 requests)  and EPA has advised us that it will be “buyer beware” until the tolerance is set. If there is a problem with the tolerance proposed by the company (and we may not know that until later in the summer) or if the package we have submitted does not pass the economic and efficacy reviews, then  all soybeans treated with Acramite would have to be crop destructed. So, at this time we will just have to wait for the review. We will keep you posted as we hear more from EPA. Also, please keep us posted on how well dimethoate and Lorsban are performing.

A couple of additional comments about spider mite control: All the new products we are testing for spider mite control, including the Acramite, will provide the best control when applied as soon as economic levels are present. Complete control may/will not be achieved with one application if populations are exploded or established at treatment time. There is no product out there that we have tested that can do it at this time using economic, labeled rates. Some have longer residual, but if you wait until high numbers are present and numerous eggs are present, you may still need multiple applications – even with the newer products. If populations are declining, you may get away with one application, but that is all dependent on weather conditions. In many cases we may be limited to one application with these newer products if we can even get a soybean label (for resistance management and residue issues, so it is critical to scout and treat in a timely manner.

Continue to watch for green cloverworm populations. No controls will be needed until you find 30% defoliation pre-bloom and 15% during bloom. As a general guideline, you should also find 10-15 cloverworms per foot of row . Unfortunately, we do not have a threshold for the number per sweep.

We continue to hear reports of spraying for soybean aphids in areas east of the typical areas – i.e. Ohio and PA.  Since our populations are migratory from the mid-west and possibly from the north, it will be important to start sampling fields for soybean aphid. You will need to look at the entire plant when sampling for aphids. The treatment threshold is 250 per plant up to growth stage R-3 with 80% of the plants at that level. You should also pay attention to predator populations that can help control aphid populations.  Numerous products are now labeled for soybean aphid including Asana, Baythroid (suppression only), Mustang MAX, Warrior, and Lorsban. Dimethoate  has not provided adequate control and Furadan 4F only has a 2ee label for the Midwestern states.



Field Crop Diseases - Bob Mulrooney, Extension Plant Pathologist, bobmul@udel.edu


Fungicides Labeled for Soybean Rust When It Appears.
Most of you are aware of the soybean rust threat to the United States soybean crop. Fortunately, as of this writing, soybean rust has yet to be found in the continental U.S. Once soybean rust is found here, the only practical control, at least in the short term, will be to apply foliar fungicides. One major hurdle we have to overcome, is that the only fungicide labeled for use on soybean in the U.S., that is also highly effective against soybean rust, is azoxystrobin or Quadris, produced by Syngenta. Everyone is in agreement that the supplies of Quadris would be depleted rapidly if no other effective products were available for farmers to use. Keep in mind that there are 73 million acres of soybean in the U.S.!

With the above situation in mind, a group of scientists, with Minnesota and South Dakota taking the lead, developed a "national section 18 application" and submitted it to the Environmental Protection Agency (EPA). The application requested approval for use of multiple fungicides (primarily triazoles) once soybean rust is found in the U.S. States were given the option to "sign on" to the section 18 application, which Delaware did beginning back in February. As of now, EPA has approved the use of myclobutanil (Laredo EC and Laredo EW [Dow Agrosciences]) and propiconazole (Bumper [Makhteshim-Agan], Propimax [Dow], and Tilt [Syngenta]) in Delaware should soybean rust be found in the U.S. and require control.

Note: the section 18 DOES NOT GO INTO EFFECT until soybean rust is confirmed in the United States. Until then, it is ILLEGAL to use any of the aforementioned section 18 fungicides on soybean in Delaware.

I expect EPA to approve additional fungicides in the next couple of months. I will keep you informed each time another section 18 fungicide is approved. However, I did think it was important to inform you now that proactive steps are being taken in preparation for the eventual arrival of soybean rust in Delaware.


The following article recently appeared in Kentucky Pest News authored by Don Hershman, Doug Johnson, and James Herbek, Kentucky Extension Specialists. With the interest in the use of Quadris on soybeans I thought it would be of interest to Delaware growers.

Last season there was considerable interest in spraying soybean in the early pod stages with a combination of Quadris (6.2 fl oz /A) + Warrior (2.56 fl oz/A). Based on our discussions with farmers, consultants and agrichemical dealers, we estimate that about 30,000 acres were sprayed in 2003. Our contacts also indicate that there is even more interest this year in light of the strong soybean market and word-of-mouth "advertising" by many farmers who experienced good results with the treatment in 2003.

In early February of this year, we wrote a fairly comprehensive Kentucky Pest News article (http://www.uky.edu/Agriculture/kpn/kpn_04/pi04020 9.htm ) on the Quadris + Warrior treatment. Not much has changed since that article was published. Two things were very obvious by the end of last season. First, the Quadris + Warrior treatment does show considerable promise, even though we have yet to account for the apparent yield impact (commonly in 3-8 bu/A range) by the treatment. By way of reminder, the results of two replicated field experiments in 2003 indicated that only the combination treatment (Quadris, 6.2 fl oz/A + Warrior, 2.56 fl oz/A), but neither treatment applied alone, significantly increased yields. However, in those same research plots, Quadris had the same impact as Quadris + Warrior in terms of disease control (stem anthracnose was controlled), and delayed maturity. Warrior, on the other hand, did not affect maturity and insect pests did not appear to be at yield-limiting levels. Yet, it took mixing Warrior with Quadris before yield increases were evident!

The second obvious finding from last year is that applying Quadris + Warrior does NOT always result in increased yields. Yes, some producers were very pleased with the yield results of the treatment last season. Others, however, were very disappointed by the apparent lack of a yield response to the treatment. Clearly applying Quadris + Warrior does not assure a yield increase, and anyone making the application this season should consider no yield response as a definite possibility. Nonetheless, based upon our research and a summary of yield data from many fields last year, it does appear that the odds favor yield increases, at least based on 2003 results.

Our research, as well as the experience of numerous farmers last year, suggests that late-planted crops and late maturing varieties may be the least likely to show an economic yield response to Quadris + Warrior. Our goal for this season is find out why applying Quadris + Warrior substantially increases yields in some situations, yet does not have a positive yield outcome in others. We watched and scouted large and small plots last year and nothing, pest wise, really floated to the surface except stem anthracnose. At harvest, stem anthracnose was very evident in almost every field we looked at, and the Quadris + Warrior treatment reduced this disease by 40- 50% in most cases. But as discussed above, Quadris alone also reduced stem anthracnose, but with no yield response. So whatever is going on is not very obvious.

Note: Delaware will have some of our own data. We are planning several small plot tests at the REC using some of these treatments. We will be reporting to you when we get the results. Stem anthracnose mentioned in the above article is also a common disease of soybean.




Grain Marketing Highlights - Carl German, Extension Crops Marketing Specialist; clgerman@udel.edu


General Comments.

USDA's July supply and demand estimates are due out on Monday, July 12th. There will likely be some position squaring going into the release of the report in market action today and tomorrow. The July '04 corn, soybean, and wheat futures contracts will be expiring soon, therefore, some of the recent price action has to take into account the sell off that occurs when traders exit their futures contract positions. The weather factor continues to be price negative as near 'ideal' weather conditions are being reported in the heart of the Corn Belt. Weekly crop condition reports continue to place near 70% of the '04 U.S. corn and soybean crops in the good/excellent category. Some farmers in the Corn Belt are reporting less than ideal growing conditions occurring, particularly for soybeans, and in some cases for corn in their neck of the woods. However, the extent of the impact on yields and the production forecasts, if any, is not likely to be known until the release of the August crop report. Corn Belt weather is forecast to turn hotter and dryer over the weekend. Commodity traders will be watching weather developments as the supply and demand forecasts are factored into commodity bidding next week. Unless we see significant adjustments made in the supply/demand balance sheets in the July report, the weather is likely to remain the dominate factor in commodity trading next week.


It might be fair to assume that production estimates for corn and soybeans forthcoming in Monday's crop report will be on line with trend line yields, resulting in record or near record production estimates for '04 U.S. corn and soybean production. We are likely to see a leveling off in corn prices occurring, at least until we work through the pollination period. We still have another month of price bidding to ration the old crop soybean supply before the August futures contract expires. This may result in short term rallies that may be used for those that need to catch up on pre-harvest forward pricing sales. If weather conditions remain ideal in the Corn Belt, things could turn ugly in a hurry with new crop corn and soybean prices drifting lower from their current levels. Some analysts were indicating this week that wheat futures are likely to be putting in their seasonal harvest lows. Perhaps the technical indicators will be able to confirm that contention as the July '04 futures contract approaches expiration.




Causes of Acidity in Soils in 2004 - Richard W. Taylor,Extension Agronomist, rtaylor@udel.edu and Sean Scanlon, Cooperative Extension Intern


During 2004, there have been numerous reports of either spots in fields or even whole fields that test out with pH’s in the range from mid-3’s to mid-4’s.  Many folks have asked why these spots have appeared and we’ve put together a list of at least some of the possible causes.


● Anion (Sulfate or SO4-2 and nitrate or NO3-, etc.) leaching due to high rainfall amounts in 2003 and accompanying cation (calcium or magnesium mostly) transport out of the root zone


● Release of hydrogen (H+) ions that cause acidity during nitrification of ammonium (NH4+) nitrogen derived from ammonium based fertilizers, urea based fertilizers, or from organic sources as the organic nitrogen is mineralized


● Nitrogen (N) fertilization practices

♦ Multiple N applications caused by N losses from heavy rainfall (denitrification or leaching).  The wet winter of 2002 followed by the wet growing season in 2003 resulted in many growers having to apply substantial quantities of N to corn several times during the growing season.  The release of H+ ions when ammonium is nitrified to nitrate and the loss of cations such as calcium and magnesium when nitrate leached would have acidified the soil.  Symptoms from this cause are most likely seen in large areas of a field or in areas of a field related to soil type differences.

♦ Overlap when putting N on fields can lead to acid strips especially on sandy or compacted soils (symptoms often appear in strips related to overlap or soil type/soil compaction/rooting depth issues).

♦ N rate changes at the end of fields when making turns while still applying N fertilizers (often seen as roughly circular to oval spots near field headlands).  See Photo 1.

♦ Equipment problems causing over-application of N (usually in strips or in small areas if the problem is detected quickly).


● Multiple cropping cycles with crops requiring high N fertilization rates.


● Acidification related to ditch spoils or other soil disturbance (see Photo 2).


● Low soil pH on former homestead site (see Photo 3).


● Sometimes on slightly sloping terrain on the lighter texture soils, you will find acid patches part way down the slope where water drains out carrying N fertilizers.  These areas can extend to the top of the slope if leaching of anions and cations is part of the problem.  They often are large oval areas and can be quite low in pH (see Photo 4).


● Infertile areas, sandy or gravelly spots in a field, areas of excessive cation (calcium and magnesium) leaching


● Areas that may not regularly receive a full rate of lime due to obstructions in a field, overlap problems, ends of fields, etc.


Certainly, the above list is not a complete list of the likely causes of either acid spots in a field or of entire fields showing lower than expected soil pH levels.  However, it should help you explain some of the problems that may be showing up this year even after an application of lime.


What can you do about this type of problem?  If you have the ability to geo-reference your field using GPS, referencing the problem areas within each field and use a soil test to determine the amount of lime needed to apply to the areas to bring them back to the pH level of the rest of the field.  If your entire field has been affected, then a new soil test and subsequent lime recommendation should help bring the field up to where it needs to be for optimum crop production.  If you do not have access to GPS equipment to map your fields and problem spots, then hand draw maps of the problem fields so you can find them in the future and treat them as a new crop management zone that you’ll manage differently (extra lime, a separate soil test, etc.) until the problem is eliminated and the zone can be integrated back into the entire field.


Other management options include trying to be as careful as possible when applying N fertilizer to avoid potential overlap areas, turn applicators off before making sharp turns at the ends of the fields to avoid uneven application, carefully monitor lime applications to be certain that they are as uniform as possible within a crop management zone, and where ditch control devices allow sub-irrigation or assist in field drainage, use these devices to limit the amount of denitrification that can occur on wet fields.






Photo 1.  Roughly oval acid soil patch in head lands of corn field following emergency lime application to rescue crop (Photo by R. Taylor).



Photo 2.  Soil acidification due to oxidation of minerals in ditch spoil on a gravelly, loamy sand corn field (Photo by R. Taylor).



Photo 3.  Acid area in field corresponding to cleared home site  (Photo by R. Taylor).



Photo 4.  Acid area in sweet corn field corresponding to where water and mobile nutrients (primarily nitrogen) emerge from sloping terrain on a very sandy soil.  The pH at this site was in mid-3 range (Photo by R. Taylor).





Photo 5.  Acid area in sweet corn field (Photo by R. Taylor).





                 Weather Summary


Week of July 2 to July 8, 2004


0.13 inches: July 5

0.01 inches: July 7


Readings taken for the previous 24 hours at 8 a.m.


Air Temperature:

Highs Ranged from 92°F on July 5 to 83°F on July 3.

Lows Ranged from 75°F on July 5 to 63°F on July 4.


Soil Temperature:

84°F average.

(Soil temperature taken at a 2 inch depth, under sod)


Web Address for the U of D Research & Education Center:  http://www.rec.udel.edu


Compiled and Edited By:

Tracy Wootten

Sussex County Extension Agent – Horticulture

University of Delaware







Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating.  Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Delaware Cooperative Extension, University of Delaware. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age or national origin.


FastCounter by bCentral

Hit Counter